!!!!!!!!!!!!!!!!!!! NOOOOOO $500 is way too much. you can get brand new rotors and pads for all 4 for much cheaper at most $300. Wires like NGK run about $50-80. Replace your pcv valve. Get new denso plugs gapped for your car. Clean and inspect your distributor/cap. If you're real handy adjust your valve clearance. Flush the oil yourself.
1.Drain
2.Pour 3-5 qts through without the plug on
3. Fill
If you dont know when the timing belt was put on:
1.Check the tension
2.Check for any wear or abnormal belt coloring
3.Check for teeth cracks
4.Just to be safe and save yourself a new engine purchase get it replaced. Then you'll know you have another 90k or so to go.